What is the shape of the Earth? An odd question, isn’t it? The world’s a globe. It’s round.

To me and you it’s obvious. We’re 20th century people. The grass is green, the sky is blue and the world is round. We’ve known it From our early childhood. But is it really all that obvious?

Go out in the country. Walk to the middle of the largest field, till all that you can see is grass and flowers to the far horizon. Does it look round? Can you see the bulge? No. It lies before you flat as a pancake right to the horizon. Every bush and tree, every tiny hillock stands out clearly. So who says the world is round?

When computers were used to calculate the surface of the earth with information from the satellites, it was found that the shape of our planet is not quite so simple. It is slightly pear-shaped. The Northern Hemisphere is stretched up a bit towards the pole, and the Southern Hemisphere is dented in. There are dents and bumps on its surface. And if you could slice the Earth through the middle at the equator the result would be a circle a little bit out of true. So it’s a bit a slightly crooked one at that. What should this shape be called?

Scientists tried out all sorts of names. Finally they chose “geoid”. This is made up of “geo”, the Greek for “earth”, and “eidos” , the Greek for “view”. So all it really means is earthlike. In fact the earth is a slightly imperfect sphere. How people found this out is a long and interesting story. And that is what this book is all about.